Child-Pornography Investigation Gets Around Service Designed to Mask Identities

WASHINGTON—Law-enforcement agencies are increasingly finding ways to unmask users of a popular Web service designed to hide identities and allow individuals to exist online anonymously.

To keep their identities secret, users and administrators of a recently shuttered child-pornography website used a network called Tor that obscures the source of Web traffic, authorities said in March. Agents from Homeland Security Investigations...